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            <small>
              <a href="#Procedure">Procedure<br></a>
              <a href="#Abstract">Abstract<br></a>
              <a href="#Required_Reading">Required_Reading<br></a>
              <a href="#Keywords">Keywords<br></a>
              <a href="#Brief_I/O">Brief_I/O<br></a>
              <a href="#Detailed_Input">Detailed_Input<br></a>

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              <small>               <a href="#Detailed_Output">Detailed_Output<br></a>
              <a href="#Parameters">Parameters<br></a>
              <a href="#Exceptions">Exceptions<br></a>
              <a href="#Files">Files<br></a>
              <a href="#Particulars">Particulars<br></a>
              <a href="#Examples">Examples<br></a>

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              <small>               <a href="#Restrictions">Restrictions<br></a>
              <a href="#Literature_References">Literature_References<br></a>
              <a href="#Author_and_Institution">Author_and_Institution<br></a>
              <a href="#Version">Version<br></a>
              <a href="#Index_Entries">Index_Entries<br></a>
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<h4><a name="Procedure">Procedure</a></h4>
<PRE>
   void el2cgv_c ( ConstSpiceEllipse   * ellipse,
                   SpiceDouble           center[3],
                   SpiceDouble           smajor[3],
                   SpiceDouble           sminor[3]  ) 

</PRE>
<h4><a name="Abstract">Abstract</a></h4>
<PRE>
 
   Convert a CSPICE ellipse to a center vector and two generating 
   vectors.  The selected generating vectors are semi-axes of the 
   ellipse. 
 </PRE>
<h4><a name="Required_Reading">Required_Reading</a></h4>
<PRE>
 
   <a href="../req/ellipses.html">ELLIPSES</a> 
 </PRE>
<h4><a name="Keywords">Keywords</a></h4>
<PRE>
 
   ELLIPSE 
   GEOMETRY 
 

</PRE>
<h4><a name="Brief_I/O">Brief_I/O</a></h4>
<PRE>
 
   Variable  I/O  Description 
   --------  ---  -------------------------------------------------- 
   ellipse    I   A CSPICE ellipse. 
   center, 
   smajor, 
   sminor     O   Center and semi-axes of ellipse. 
 </PRE>
<h4><a name="Detailed_Input">Detailed_Input</a></h4>
<PRE>
 
   ellipse        is a CSPICE ellipse. 
 </PRE>
<h4><a name="Detailed_Output">Detailed_Output</a></h4>
<PRE>
 
   center, 
   smajor, 
   sminor         are, respectively, a center vector, a semi-major 
                  axis vector, and a semi-minor axis vector that 
                  generate the input ellipse.  This ellipse is the 
                  set of points 
 
                     center + cos(theta) smajor + sin(theta) sminor 
 
                  where theta ranges over the interval (-pi, pi]. 
 </PRE>
<h4><a name="Parameters">Parameters</a></h4>
<PRE>
 
   None. 
 </PRE>
<h4><a name="Exceptions">Exceptions</a></h4>
<PRE>
 
   Error free. 
 </PRE>
<h4><a name="Files">Files</a></h4>
<PRE>
 
   None. 
 </PRE>
<h4><a name="Particulars">Particulars</a></h4>
<PRE>
 
   CSPICE ellipses serve to simplify calling sequences and reduce 
   the chance for error in declaring and describing argument lists 
   involving ellipses. 
 
   The set of ellipse conversion routines is 
 
      <a href="cgv2el_c.html">cgv2el_c</a> ( Center and generating vectors to ellipse ) 
      <b>el2cgv_c</b> ( Ellipse to center and generating vectors ) 
 
   A word about the output of this routine:   the semi-major axis of 
   an ellipse is a vector of largest possible magnitude in the set 
 
      cos(theta) vec1  +  sin(theta) vec2, 
 
   where theta is in the interval (-pi, pi].  There are two such 
   vectors; they are additive inverses of each other. The semi-minor 
   axis is an analogous vector of smallest possible magnitude.  The 
   semi-major and semi-minor axes are orthogonal to each other.  If 
   smajor and sminor are choices of semi-major and semi-minor axes, 
   then the input ellipse can also be represented as the set of 
   points 
 
 
      center + cos(theta) smajor + sin(theta) sminor 
 
   where theta ranges over the interval (-pi, pi]. 
 
 </PRE>
<h4><a name="Examples">Examples</a></h4>
<PRE>
 
   1)  Find the semi-axes of the limb of an ellipsoid. 
 
          #include &quot;SpiceUsr.h&quot;
                  .
                  .
                  .
          /.
          Our viewing location is viewpt.  The radii of the 
          ellipsoid are a, b, and c. 
          ./
          <a href="edlimb_c.html">edlimb_c</a> ( a, b, c, viewpt, &amp;limb );

          <b>el2cgv_c</b> ( &amp;limb, center, smajor, sminor ); 
 </PRE>
<h4><a name="Restrictions">Restrictions</a></h4>
<PRE>
 
   None. 
 </PRE>
<h4><a name="Literature_References">Literature_References</a></h4>
<PRE>
 
   None. 
 </PRE>
<h4><a name="Author_and_Institution">Author_and_Institution</a></h4>
<PRE>
 
   N.J. Bachman   (JPL) 
 </PRE>
<h4><a name="Version">Version</a></h4>
<PRE>
 
   -CSPICE Version 1.0.0, 12-JUN-1999 (NJB)
</PRE>
<h4><a name="Index_Entries">Index_Entries</a></h4>
<PRE>
 
   ellipse to center and generating vectors 
 </PRE>
<h4>Link to routine el2cgv_c source file <a href='../../../src/cspice/el2cgv_c.c'>el2cgv_c.c</a> </h4>

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   <pre>Wed Jun  9 13:05:23 2010</pre>

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